Engine systems may utilize recirculation of exhaust gas from an engine exhaust system to an engine intake system (intake passage), a process referred to as exhaust gas recirculation (EGR), to reduce regulated emissions and improve fuel economy. An EGR system, such as a low-pressure EGR system, may include various sensors to measure and/or control the EGR. As one example, an engine intake system may include an intake gas constituent sensor, such as an oxygen sensor, which may be employed during non-EGR conditions to determine the oxygen content of fresh intake air. During EGR conditions, the sensor may be used to infer EGR based on a change in oxygen concentration due to addition of EGR as a diluent. One example of such an intake oxygen sensor is shown by Matsubara et al. in U.S. Pat. No. 6,742,379. However, the accuracy of EGR estimates using the intake oxygen sensor may be reduced during boosted engine operation and purge conditions when hydrocarbons are flowing through the intake system. EGR flow may then be estimated using alternate EGR sensors. For example, the EGR system may also include differential pressure over valve (DP) sensor positioned around an EGR valve for estimating EGR flow based on a pressure difference across the EGR valve and a flow area of the EGR valve. EGR flow estimates may then be used to adjust a position of the EGR valve and therefore adjust an amount of EGR provided to the engine.
As one example, a flow area of the EGR valve may change when the EGR valve temperature changes due to changes in EGR temperature. More specifically, thermal expansion or contraction of the EGR valve may cause a change in the EGR valve flow area. This change in EGR valve flow area may impact the EGR flow estimate, and thus EGR control, based on measurements from a DPOV system including the DP sensor. The inventors herein have recognized that error in EGR flow estimates using the DPOV method may increase as a temperature difference between a stem and body of the EGR valve increases.
In one example, the issues described above may be addressed by a method for adjusting an exhaust gas recirculation (EGR) valve based on an estimate of EGR flow, the EGR flow estimated based on a pressure difference across the EGR valve and an adjusted valve flow area, the adjusted valve flow area based on a first temperature difference between a stem and body of the EGR valve. In this way, changes in a flow area of the EGR valve due to thermal expansion or contraction may be determined and subsequent EGR flow estimates may be corrected based on the adjusted valve flow area, thereby increasing an accuracy of EGR flow estimates and resulting engine control.
As one example, a second temperature difference between a stem and body of the EGR valve may be determined when the EGR valve is closed. The difference between the between the second temperature difference of the stem and body of the EGR valve and the first temperature difference between the stem and body of the EGR valve may be used to provide change in EGR valve flow area. The change in EGR valve flow area may be used to correct EGR valve area estimates. Corrected EGR valve area estimates may be used for subsequent EGR flow estimates.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.